1. Field of the Invention
The present invention relates generally to a centrifugal fan impeller structure, and more particularly to a centrifugal fan impeller structure, which can reduce noise in operation of the centrifugal fan.
2. Description of the Related Art
Along with the rapid development of electronic industries, the performance of the electronic components has been more and more enhanced. The electronic components have operated at higher and higher speed. In the meantime, the heat generated by the electronic components has become higher and higher. In case the heat is not dissipated in time, the operation performance of the electronic components will be deteriorated. In some more serious cases, the electronic components may even burn out. In order to dissipate the heat, a miniaturized centrifugal fan is installed in a limited space of the system for carrying away the heat. The centrifugal fan includes a frame body, a fan hub and multiple blade bodies annularly disposed around outer circumference of the fan hub. Each of upper and lower sides of the frame body is formed with an air inlet. A lateral side of the frame body is formed with an air outlet. In operation, the blade bodies rotate to drive the ambient air to flow. The axial airflow going into the frame body from the air inlet is turned to radial airflow, which is exhausted from the air outlet.
When the centrifugal fan operates, the non-uniform wake flowing out from the fan impeller will interact with the tongue to make noise. In the case that the gap between the fan impeller and the tongue is relatively narrow, the noise will be affected by the tongue oscillation caused by the impact of the non-uniform wake onto the tongue and the pressure difference around the tongue. In the case that the gap is 20% the radius of the fan impeller, only the non-uniform wake will affect the major noise source and the non-uniform wake only has little affection on the major noise source. In addition, the wake strength can be lowered by means of adding short vanes between the blades. This can minimize the affection of the non-uniform wake on the pressure turbulence and the noise. According to the above, the conventional centrifugal fan has the following shortcomings:                1. The structural design is limited.        2. The conventional centrifugal fan cannot be flexibly designed according to the characteristics.        3. The noise is loud.        